Former British prime minister Tony Blair advised a key executive in Rupert Murdoch’s newspaper empire over phone hacking, a London court has heard.

Blair also offered to be an “unofficial” adviser to Murdoch and his son James at the height of the scandal which led to the closure of the News of the World newspaper in July 2011.

An email written by Rebekah Brooks, then chief executive of Murdoch’s British newspaper group, News International, described an hour-long phone call with Blair in which he allegedly told her to “tough up”.

The email was shown to the jury at the end of almost four months of prosecution arguments in the phone-hacking trial, in which Brooks is expected to take the stand later this week.

The 45-year-old denies charges of conspiring to illegally access voicemails, bribing public officials and trying to hide evidence from police.

Brooks’ email was addressed to James Murdoch, Rupert Murdoch’s son and then chairman of News International.

Brooks described how Blair allegedly told her: “Keep strong and definitely sleeping pills. Need to have clear heads and remember no rash short-term solutions.”

He also reassured her that “it will pass. Tough up”.

Brooks wrote that Blair said he was “available to you (James Murdoch), KRM (Rupert Murdoch) and me as an unofficial adviser but needs to be between us”.

The email also says Blair recommended that Brooks set up an independent inquiry to investigate senior News of the World managers.

Brooks is expected to give evidence on Thursday when lawyers for the seven defendants begin making their case.

She is among three defendants facing charges of phone hacking, including her former lover and deputy at the News of the World, Andy Coulson, who replaced her as editor in 2003.